Centralized traffic controlling system



N.D.PRESTON CENTRALTZED TRAFFIC CONTROLLING SYSTEM Dec. 6, 1938.

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u in Patented Dec. 6, 1938 UNITED STATES PATENT OFFICE CENTRALIZED TRAFFIC CONTROLLING SYSTEM Application January 30, 1931, Serial No. 512,257

33 Claims.

This invention relates to systems for governing traffic on railroads, and more particularly to systems known as centralized trafiic control sys ems.

In a centralized traffic control system of the type contemplated by this invention, the switches and signals at various points along a railroad track, throughout an extended territory, are placed under the control of an operator in a central control oflice, in such a way that the operator may at will change the position of the switches, subject to automaticapproach and detector locking control circuits, which prevents unsafe operation of any switch, and may also hold at stop any of the signals, or allow them to clear, dependent upon the position of the associated switches, and also provided the location of trains makes it safe for such a signal to indicate proceed. In such a type system, it is desirable that the operator be fully and accurately informed of the movement of trains, and also of the operation of the switches and signals which he controls, in order that he may direct train movements most efficiently. For this purpose, various indications should be transmitted to the control oifice to show, among other things, the presence or absence of a train on a particular section of track, the over and locked position of a switch, and the clear or stop indications of a signal.

In accordance with this invention, the indications of the condition of a switch and the indications displayed by its associated signals are transmitted to the control ofiice in the same way heretofore employed in systems of this type; but instead of displaying these indications separately, so that the operator has to make a mental summation of these indications, so to speak, in order to determine if this switch and its signals-have been operated as he desired, it is proposed to provide route and no route indicating lamps, or equivalent means, and a movable miniature switch point, or the like, indicating the position of the switch. These indicating means or devices are jointly controlled by indications received from the field and by the position of the switch and signal control levers, in such a way that the operator can easily and quickly tell if a route for train movement has actually been set up in the field and the signal cleared, the direction in which trains have been signalled to move over the switch, the position of the switch, and such other information as the operator needs to guide him in the manipulation of the control levers,

tions of their control levers.

Stated more specifically, in accordance with this invention, a route lamp indicating direction by an arrow, or the like, and located adjacent each switch on the track diagram of the railroad under the operators supervision, is 5 lighted on the control board before the operator, when that track switch is over and locked in a position corresponding with the position of the switch control lever, and when a signal in the field has actually been cleared for trains to move in the direction indicated by this lamp. Thus, when such a route lamp is lighted, the operator knows that the switch and its associated signals in the field have properly responded to the control he has established by positioning the control levers, and that a route for trains has actually been set up over the switch in the normal or reverse position indicated by the miniature switch point, and in the direction indicated by the route lamp lighted. If a route lamp adjacent the switch is not lighted for either direc tion, the operator knows that no route has been set up for trains to move over that switch, and that further manipulation of the control levers may be necessary to set up this route. The no route indication is displayed when, and so long as, the corresponding switch and its signals in the field are out of correspondence with the posi- This no route indication is displayed whenever the operator moves either the switch or the signal control lever to a position out of correspondence with the corresponding switch and signals in the field, and is maintained displayed until said switch and signals have operated to the desired positions. If this no route indication is displayed for a time longer than that required for the switch and signals to operate, then the operator knows that these devices in the field have not properly operated for some reason, and that further action may be necessary to permit trains to move. Such a no route indication makes it necessary for the operator to watch for changes in the standing indications of the position of a switch and the indications of signals, now ordinarily used, in order to determine if the system has operated as desired.

According to this invention, the indications of the presence of trains in various track sections are displayed in the usual way by lighting small indicating lamps on the track diagram; but provision is also made for-controlling the lighting of these lamps in such a way that each new indication may be readily identified by the operator, and will remain displayed, irrespective of the continued presence of the train, until recognized by the operator. Stated more specifically, when a train enters a track section, the corresponding indicating lamp is flashed intermittently, thereby distinguishing it from other indications of track section occupancy which may have been standing for some time; and this flashing of the light continues, until the operator manipulates a push button, or equivalent means, as an act of recognition of this new indication of a train movement.

Another feature of this invention relates to means for improving the operation of selective type communication systems by suppressing or holding back initiation of the operation of the system to transmit indications from a particular field station, upon change in the condition of a switch or its associated signals at that station, until all of the conditioned operations of the switch and signals have taken place, so that all indications of the new conditions may be transmitted to the control office during one operating cycle. In connection with this feature of the invention, it is assumed that indications of the locked or unlocked condition of the switch, or its over and locked position, and of the clearing or putting to stop of a signal, are all to be transmitted to the control office. In such a case, since the operation of the switch and its associated signals take place successively, with operating times between the successive operations, these separate indications would ordinarily be transmitted to the control ofiice one at a time during separate operating cycles; and several operations of the system would be necessary to transmit to the control oiiice a number of indications which are of no interest to the operator until all have been received. This indication suppression feature of this invention reduces the number of operating cycles required, upon change in a route at a station, to transmit to the control office the necessary indications from that station, thereby avoiding any objectionable delay in the transmission of indications from other stations.

This invention also embodies means for transmitting, during different operating cycles, either one of two groups of indications, according to the changes that may have taken place to necessitate transmission of a new indication in one group or the other. More specifically, it is proposed to transmit during one operating cycle the indications of the operated condition of a switch and its associated signals as one group, and the indications of the presence of a train on certain track sections as another group. In this way, the number of indications to be transmitted on one operating cycle is reduced and is more nearly in accord with the number of controls which have to be transmitted for the control of a switch and its associated signals. In other words, by transmitting the indications in groups as proposed in accordance with this invention, the number of steps in an operating cycle is made substantially the same for both controls and indications.

These characteristic features of the invention, thus briefly stated, will be explained more in detail in the following description of one embodiment of the invention; and various other characteristic features, functions and advantages of a system embodying this invention will in part be pointed out, and in part apparent as the description progresses.

In the accompanying drawings, the invention has been shown applied to one switch and its associated signals, such as used at one end of a passing siding; but it should be understood that the invention is not limited, as thus shown, to the control of one switch and its signals, but may be extended for any desired number of switches and signals, and may be readily applied to all types of track layouts.

In describing the invention in detail, reference will be made to the accompanying drawings, in which similar parts throughout the several views are designated by similar reference characters provided with distinctive exponents, and in which:

Fig. 1 illustrates the apparatus and circuit arrangements provided for a typical control office having indication means constructed and arranged according to the present invention.

Fig. 2 illustrates the apparatus and circuit arrangements employed at a typical field station for providing the information of the traffic governing conditions at a single track switch in accordance with the present invention, and adapted to be associated with the apparatus employed in the control office.

Fig. 3 illustrates the apparatus and circuit arrangements employed in the system for starting it into operation at a field station. The relays and contacts of this figure correspond to the relays and contacts of Fig. 3 of the Patent No. 2,129,183 dated September 6, 1938 granted to N. D. Preston et al.

Fig. 4 illustrates the line circuit organization connecting the control office and the several field stations and corresponds to the above-mentioned Patent No. 2,129,183.

Fig. 5 illustrates the stepping relay bank proposed to be employed with the system of the present invention, which Fig. 5 corresponds to Fig. 5 of the above-mentioned Patent No. 2,129,- 183.

Fig. 6 is an illustration of the circuit arrangement for transmitting controls over the line circuit illustrated in Fig. 4, and these circuits are taken from the above mentioned Patent No.

For the purpose of simplifying the illustration and facilitating in the explanation, the various parts and circuits constituting the embodiment of the invention have been shown diagrammatically and certain conventional illustrations have been employed, the drawings having been made more with the purpose of making it easy to understand the principles and mode of operation, than with the idea of illustrating the specific construction and arrangement of parts that would be employed in practice. Thus, the various relays and their contacts are illustrated in a conventional manner, and symbols are used to indicate connections to the terminals of batteries or other sources of electric current, instead of showing all of the wiring connections to these terminals. The symbols and are employed to indicate the positive and negative terminals respectively of suitable batteries or other sources of direct current; and the circuits with which these symbols are used, always have current flowing in the same direction. The symbols (B+) and (B) indicate connections to the opposite terminals of suitable batteries or other direct current source which has a central or intermediate tap designated (ON); and the circuits with which these symbols are used, may have current flowing in one direction or the other depending upon the particular terminal iii) used in combination with the intermediate tap (CN) While certain features of the invention are applicable to, and useable with, any type of communication system for centralized trafiic control, Whether obtained by direct line wire control or by some form of a selective type communication system, the specific embodiment of the invention illustrated has been shown in a form adapted for use with a selective communication system of the duplex coded type, shown and described in detail in the prior patent to N. D. Preston et al, Patent No. 2,129,183, dated September 6, 1938. Thus, before considering the structure and mode of operation of the parts constituting this invention, it becomes necessary to explain some of the features of this particular duplex coded type of communication system, insofar as material to an understanding of the present invention, reference being made to said prior aplication for other details of the structure and operation of such a duplex coded communication system not directly related to the features of this invention.

Communication part of the system.-The com- I munication part of the centralized traffic control system comprises a transmitting and receiving equipment located in the control ofiice and interconnected with transmitting and receiving equipments located at the various field stations. For example, a control oifice transmitting and receiving equipment has been indicated as included within a dotted rectangle In of Fig. 1, and a field station transmitting and receiving equipment has been indicated as included within a dotted rectangle ll of Fig. 2, with these equipments showing only those parts which are directly related to the devices and functioning of the particular embodiment of the present invention.

Fig. 3 illustrates the arrangement proposed for starting the system into operation from a field station. The relays and contacts of this figure illustrate corresponding relays and contacts of Fig. 3 of the above-mentioned Patent No. 2,129,183, with the preceding numeral 3 added to the corresponding reference characters. Relay 3G8 is relay GS of Fig. 2 of the present application and contact 32! is contact 2! of Fig. 2 of the present application; It will thus be obvious that the energization of either relay CH or GS of Fig. 2 will complete a circuit for picking up relay 3P of Fig. 3, which in turn de-energizes the message line for dropping relay iM of Fig. 4 which starts the system into operation in any approved manner, such for example as illustrated by relay M of Fig. 1B of the above-mentioned Patent No. 2,129,183.

Fig. 4 illustrates the line circuit organization proposed, which figure corresponds to Fig. 4 of the above-mentioned Patent No. 2,129,183. Corresponding reference characters have been used, with the addition of the prefix 4 in the present drawings. The operation of this line circuit for impulsing, transmitting controls and indications, selection of stations and the registration of stations is explained in detail in the above-mentioned Patent No. 2,129,183.

Fig. illustrates the stepping relay bank proposed to be used in the system of the present invention, which figure corresponds to Fig. 5 of the above-mentioned Patent No. 2,129,183. The relays and contacts have been given reference characters which correspond to Fig. 5 of the Patent No. 2,129,183, but with the preceding numeral 5 added. The operation of this stepping bank is explained in detail in the above-mentioned Patent No. 2,129,183. The stepping bank at the station-operates in a manner similar to that in the ofiice and consequently it is not believed necessary to show the circuits of the field station stepping bank in detail. The numbers I, 2, 3 and 4 ap pearing within the blocks which illustrate the stepping relays in Figs. 3 and 5 indicate the first, second, third and fourth stepping relays respectively. While the circuits illustrated in Fig. 5 showthe operation of the first four stepping relays only, it will be understood that the remaining relays of the bank, such as 5, 6, i and 8 of Fig. 2 and e, f, g, and h of Fig. 1, operate in response to additional steps of the cycle in the same manher as those illustrated.

Fig. 6 is a diagrammatic illustration of the proposed arrangement for transmitting controls over the stepping and control line in accordance with the polarity of the impulses applied to this line as selected, for example, by the position of lever BSML which corresponds to lever SNL of Fig. 1 of the present application and lever SML of g. 1A of the above-mentioned Patent No. 2,129,183. The relays and contacts of Fig. 6il1ustrate corresponding relays and contacts of Fig. 1A, Fig. 1B and Fig. 2 of the Patent No. 2,129,183, with the preceding numeral 6 added to the corresponding reference characters. Reference may be made td the above-mentioned Patent No.

2,129,183 for a detailed explanation of the control transmission operation illustrated in Fig. 6.

In this duplex coded type of communication system, three line wires connect the control ofiice with the several field stations forming a series stepping and control circuit, and a series message circuit, with a common return connection. In the accompanying drawings these three line wires are designated I2, l3 and Id. The transmission of controls from the control ofiice to one selected station, and/or the transmission of new indications, if any, from that station or some other station, back to the control oifice, takes place simultaneously during the execution periods of a predetermined number of steps resulting from the successive energizations of the stepping circuit at time-spaced intervals, this being conveniently termed an operating cycle. In the beginning of such an operating cycle, a slow-acting relay SL. in the control ofiice (see Fig. 1) and a similar relay SL at each field station (see Fig. 2) are energized, and maintained energized throughout the operating cycle. The application of the successive impulsesof the cycle to the stepping circuit causes the operation of the stepping relays at the control ofiice and at each field station, one step for each impulse. The time periods or spaces between the successive impulses of a cycle are conveniently termed execution periods during which periods the controls and indications can be suitably transmitted or executed. These execution periods are marked off by a quick acting relay LR in the control ofiice (see Fig. 1), and a quick acting relay LR (not shown) at each field station.

The system is normally at rest, but is set into operation by the operator to establish communication with a selected station by actuation of a starting button SB (see Fig. 1) associated with the control levers for that station. The system may also be set into operation independently of the operator, whenever a change takes place at any one of the field stations requiring the transmission of indications. Referring to Fig. 2, the system is thus set into operation, whenever the change relay OH, or the group selecting relay GS,

are energized to close their contacts 20 and 2|; The detail apparatus and circuits for initiating operation of the system upon actuation of a starting button SB for a station, or upon energization of the relay CH or GS at a field station, are disclosed in the application of N. D. Preston et al., above-mentioned, and since it is sufficient for an explanation of the present invention to understand that such operation takes place, no attempt has been made to illustrate or describe such detail circuits and apparatus.

The operating cycle of this duplex coded communication system consists of a station selecting part and a transmitting part. During the station selecting part of the operating cycle, the station to receive controls from the control ofiice is selected in the manner explained in detail in said application of Preston et al., above mentioned, resulting in the energization of the relays SO and TR shown in Fig. 2, which are at that station. Also, during this station selecting part of the operating cycle, one of the several field stations having new indications to transmit is registered in the control office, this condition being manitested by the energization of a station registering relay in the control office, such relay as C (see Fig. 1), and the energization of the relays SI and TR. at the corresponding field station, such for example as shown in Fig. 2. During the transmitting part of the operating cycle, a series of stepping relays in the control ofiice, such as the relays d, e, j, g and h (see Fig. 1), and a similar series of stepping relays at the station selected for outgoing controls and/or at the station registered in the control office for incoming indications, such as the relays 4, 5, 6, 1 and 8 (see Fig. 2), are energized sequentially one at a time in synchronism by impulses applied to the stepping circuit; and on each of these successive steps either one of two distinctive controls, or two distinctive indications, may be simultaneously transmitted from or to the control office, all

in a manner fully explained in said application of Preston et al., above-mentioned.

For the purpose of understanding the present invention, it is not necessary to explain in detail how these controls are transmitted in this duplex coded type of communication system; and it is sufficient to note that such transmission of either one of two controls on each step results in positioning the contact finger of a polar relay in one extreme position or the other, in correspondence with the position of the corresponding control lever. Each of these polar function control relays at a field station is of the dead-beat or magnetic stick type, so that its contact fingers are held, in the position to which they were last operated, by a permanent magnet or equivalent means until they are operated to the other position.

In a. similar way, the transmission of one of two indications on each step results in positioning the contact finger of a magnetic stick polar relay in the control ofiice to one extreme position or the other, in accordance with the position or condition of the corresponding device being indicated. In this transmission of indications from the several field stations, in addition to the registration of these stations in the control ofiice one at a time by the energization of a corresponding station registering relay, such as the relay 0 shown in Fig. l, and the energization of the relays SI and TR at the particular station thus registered, there is also, in accordance with this invention, a selection of the group of indications to be transmitted on the particular operating cycle then in effect; and for this purpose there is a group selecting relay GS in the control ofiice for each station, and a group selecting relay GS at each field station. Typical examples of the transmission of indications will be explained more in detail hereinafter.

Keeping in mind this general organization of the complete communication system contemplated in connection with the particular embodiment of the invention illustrated, and particularly the fact that controls and indications may be transmitted to and from any one of several field stations, one at a time, during successive operating cycles, consideration may now be given to an explanation of the present invention as if it were applied to any one station, as shown in the accompanying drawings.

Control oflice equipmcnt.The control ofiice (see Fig. 1) includes'besides a transmitting and. receiving equipment, a control machine having a group of control levers for each field station, a miniature track layout corresponding in every way to the actual track layout in the field, and various indicating lamps or equivalent devices, together with apparatus and circuits to accomplish proper functioning of the system. Fig. 1 illustrates diagrammatically a portion of such a control machine for one track switch, cross-over, or the like.

This apparatus for one track switch at a field station comprises a switch machine control lever SML, a signal control lever SGL, a starting button SB, and a cancelling key CK.

The movement of the lever SML to one extreme position or the other results in the normal or reverse control of the corresponding switch at the corresponding field station, through the medium of the communication system; and the movement of signal control lever SGL from the intermediate or vertical position shown, corresponding to signals at stop, to the right or left clears the signals over the switch in an east or west direction respectively. The starting button SB, when momentarily actuated by the operator, results in the initiation of the communication system into operation for the transmission of the controls associated with that station, as set up by the levers SML and SGL.

A miniature track diagram corresponding with the actual track layout in the territory under the supervision of the operator, is preferably made a part of the control machine, and positioned adjacent the control levers for the several field stations. As representative of such a track diagram, (see Fig. 1) a portion of track together with one pivoted miniature track switch point is is shown to represent the actual track and track switch TS located at the field station shown in. Fig. 2. The position of the track switch TS is indicated upon the track diagram by the movement of the miniature switch point member ts to normal or reverse positions, as operated by electro-magnetic means hereinafter pointed out.

The presence of a train on different portions of the track adjacent the switch is preferably indicated by small lamps of the telephone switchboard type, located on the track diagram, these lamps being lighted when a train is present on the corresponding track section. As illustrated in Fig. 1, a lamp OSL is lighted to indicate the presence of a. train on the usual detector track circuit associated with the switch, lamps EAL and WAL are lighted to show the presence of a train approaching the switch from the east and west respectively, and a lamp PSL is lighted when a.

train is present on the passing siding or turn-out track.

Each of these indicator lamps is first illuminated when a train enters the corresponding track section in the field which indication is initially displayed by a flashing of the corresponding indicator lamp until the operator has acknowledged the presence of the train by pressing the cancelling key CK. The indicator lamp is then steadily illuminated until the train leaves the section. If the train leaves the section prior to the acknowledgment by the operator, the indicator continues flashing until acknowledged.

The two route indicators, characteristic of this invention, are preferably small indicating lamps WRL and ERL located adjacent to the track switch, and provided with arrows, or equivalent direction indicating means, which is displayed when the lamp is lighted.

The no route indicator of this invention is also preferably an indicating lamp NRL, located adjacent the track switch on the track diagram, and having a color distinctive from the other indicating lamps. These various indicating devices are controlled by magnetic stick polar indication relays IR, which are operated by means of the communication system to positions corresponding with the position or condition of the device in the field being indicated. The indication relays IR, 1R IE and IE respond to the presence of a train on their corresponding track sections in the field; while relay 1R responds to the east governing signals at clear or stop; relay IE to the west governing signals at clear or stop; relay IR to the position of the track switch; and relay IR to the track switch locked or unlocked.

In the case of those indication relays IR which are associated with track section occupancy indications, as for example relays IR, 1R IE and IR a storing relay SR and an acknowledging stick relay AS are associated therewith in order to provide that the indication originally displayed shall be held over until the operator acknowledges such new indication, although the train may have passed from the associated track section. More specifically, the relay 1R controlled in accordance with the east approach track section, together with relays SR and AS are shown as controlling the east approach indicator lamp EAL. In a similar manner, the relays IR, IR and 1H with their associated stick and acknowledging relays are employed to control their respective indicator lamps OSL, WAL and PSL, such control being merely indicated for the sake of simplicity in the drawings.

A contact 25 is provided to continuously open and close so as to alternately place upon and remove energy from a flashing bus 28. This contact 25 is conventionally shown as operated by a cam member which may be continuously operated by a suitable electric motor. It is to be understood, however, that any other suitable means may be employed for this purpose, such for example as a flashing relay operated only as required.

Two directional stick relays WS and ES are employed for maintaining the route indicating lamps energized, although a train may have passed over the OS track section putting the associated signals to stop, until the operator manually causes the signals to remain at stop. I

The control of the indicating means on the control board in accordance with this invention, also involves an out-of-correspondence relay 0C.

Field station equipment.With reference to the typical field station shown in Fig. 2, a turn-out track having rails 21 is connected to the main track having rails 28 by means of a track switch TS. The track switch TS is suitably controlled from one extreme locked position to the other by any suitable type switch machine (not shown), such for example as shown in the patent to W. K. Howe, Patent No. 1,466,903, dated September 4,

1923, which switch machine is controlled by a switch machine relay SMR with such control subject to the associated signalling system and suitable approach locking means. The switch machine relay SMR is in turn controlled in accordance with the position of the switch control lever SML in the control otfice through the medium of the communication system.

' The switch machine (not shown) thus remotely controlled by the operator, is preferably provided with a dual control selector, such as disclosed in the patent granted to W. K. Howe, Patent No. 1,852,573 dated April 5, 1932, so that a member of a train crew can locally operate the track switch for local train movements, as desired, after first obtaining permission from the operator by telephone, or the like.

A portion of the main track adjacent the track switch TS and the fouling portion of the turnout track is included in a detector track section having the usual battery and track relay T associated therewith, which section is separated from the rest of the track by the usual insulated joints. East of the detector track section is an east approach track section having its battery and track relay T West of the detector track section is a west approach track section having its battery and track relay T A track section for the turn-out track is also provided with a track battery and a track relay T These track relays besides serving to furnish suitable approach and detector track section protection for the track switch TS, also serve to indicate the presence of trains in the control ofiice through the medium of the communication system.

Signals I and IA serve to govern east bound trailic over thetrack switch TS from the main track or the turn-out track respectively; while signals 2 and 2A serve to govern west bound traffic over the track switch TS on the main track or onto the turn-out track respectively. These signals l-IA and 2--2A, arranged to control train movements over the track switch TS in the usual way in accordance with recognized practice, are respectively controlled by signal control relays lFlAF and 2F-2AF which are selected in accordance with the position of the track switch TS and the direction relay DR; while their energization is dependent upon the relay SR. and trafiic conditions in accordance with the principles of automatic block signal systems, all in a manner shown and described, for example, in the prior patent of S. N. Wight, Patent No. 2,082,436 dated June 1, 1937. Although these signals have been shown as being of the color light type, it is to be understood, however, that they may be of the semaphore type, or any other suitable type railway signal.

The relays SMR, SR and DR, which are controlled over the communication system in accordance with the position of the levers SML and SGL, as more specifically pointed out in the above mentioned patent granted to N. D. Preston et al., Patent No. 2,129,183 'dated September 6, 1938, are of the polar magnetic stick type, which maintain their contacts in the last energized position as determined by the polarity of the last energization regardless of subsequent deenergization.

The position of the track switch TS is indicated by the usual switch repeating relay WP which is of the polar-neutral type relay energized with a particular polarity in accordance with the position and locked condition of the track switch TS through the usual switch box or point detector mechanism (not shown). The energization of this relay WP is also governed in accordance with the operated condition of the dual selector, when such a mechanism is employed in conjunction with the switch machine.

The signals llA and 2--2A are indicated as being at stop by the energization of the relay M which is controlled through a series of back contacts on the signal control relays lF-IAF and 2F2AF. If semaphore signals were employed, the contacts controlling the M relay would be located within the signal mechanisms.

An out of correspondence relay 0C is employed to indicate, when energized, that the traffic controlling devices at this location are in correspondence with the controls established by the operator in the control ofiice, as represented at the field station by the relays SMR and SR. A control relay CL is provided to be energized when the field station is receiving controls from the central control office.

Inasmuch as the detector track section, having the track relay T, is comparatively short, a light engine or a short train might easily pass over this section before the communication system, particularly in the case of a station selective type communication system, could transmit indication of the presence of the train upon this section. Thus, a stick relay ST is associated with the track relay T to store its deenergized condition; while also associated therewith is a cancelling relay CR. which is energized when the stored condition in the stick relay ST has been transmitted.

As the track sections associated with the relays T T and T are comparatively long, it is considered unnecessary to provide such storing and cancelling means. However, should the conditions of practice require such 'means, it is obvious that similar means can be associated with each of these relays in a similar manner as provided for the relay T.

A change in track circuit conditions causes the change relay CH to be energized by reason of momentary contacts on the track relays T T T and the storing relay ST; while a change in the conditions of the traffic controlling devices causes the relay GS to be energized by reason of two slow acting relays AX and BX together with suitable circuits.

It is believed that the nature of the invention, its advantages, and characteristic features can be best understood with further description being set forth from the standpoint of operation.

Operation of the system Before discussing the detail performance and mode of operation in the various steps included in the operation of the system under different conditions and pointing out the circuits involved, it would appear to be expedient to outline briefly the general scheme of operation.

This system is illustrated as operable by use of a communication system of the station selective type as heretofore pointed out. While such a selective type system could be operated continuously, it is preferably arranged to be normallyat rest when no controls are to be transmitted from the co'ntroloffice, or no new indications are to be communicated to the control office. The relays and circuits are shown in the positions assumed when the system is in its normal condition of rest, with the communication system so conditioned that it may be initiated into operation for the transmission of control impulses and/or indication impulses. When thus set into operation, the system goes through what is con veniently termed an operating cycle and then comes to rest again.

During each operating cycle of the system, new controls may be transmitted to any station and new indications may be received either from that station or some other station, and the system continues to go through these operating cycles so long as there are new controls or indications to be transmitted.

The whole operating cycle may be said to be divided into two parts, the first of which is employed for selecting and/or registering the station and the second of which is employed for the actual transmission of the controls and/or indications.

The transmission of controls to a field station is accomplished by first positioning the control levers, or other circuit controllers, and then initiating the system into operation by actuating the associated starting button. This procedure can be varied to suit the particular type communication system employed. For example, in some systems the movement of a control lever is sufficient to initiate the system.

During the station selecting part of the cycle thus initiated, the station selecting relay S0 is selectively conditioned in accordance with the code call transmitted. If the station is selected by the continued energization of the relay SO, the transfer relay TR is energized at the end of the station selecting partof the cycle. The system continues to operate for the transmission of controls to the function control relays, such for example as relays SMR, DR and SR, the details of which are immaterial to the present invention. The arrangement illustrated in Fig. 6 shows one method of selectively controlling the SMB relay.

The transmission of indications from a field station may be accomplished by initiation of the system at the field station. If a change in track circuit conditions occurs, the relay CH is energized; while if a change in traffic controlling device conditions occurs, the relay GS is energized. In the event that either of these relays is energized, the system is caused to operate through one complete cycle; while, if both of these relays are energized, the system is caused to operate through two complete cycles.

The energized or deenergized condition of the group selecting relay GS determines what group of indications is to be transmitted for that cycle. If the change relay CH is energized and the group selecting relay GS is deenergized, track circuit indications are transmitted; but, if both relays are energized, indications of the traffic controlling devices are transmitted during that cycle of operation and the track circuit indications are transmitted on a subsequent cycle. This feature is provided by a stick circuit for the relay CH which is closed during the operation of the system while the relay GS is energized. If the relay GS is energized and the relay CH is not energized, the indications associated with the trafiic controlling devices are of course transmitted.

During the station selecting or registering part of the operating cycle incurred by initiation from a field station, the station selecting relay SI is selectively conditioned at the particular station corresponding to the resulting code call transmitted to the control office. If the station is selected by the continued energization of the relay SI, the relay TR is energized at the end of the station selecting part of the cycle. The system continues to operate for the transmission of indications from the selected station.

During the station selecting part of a cycle initiated in the field, the resulting code call transmitted to the control oflice registers the selected station by the energization of the corresponding station relay C The relay C causes the indication impulses transmitted on the second part of the cycle to be applied to the indication relays IR corresponding to the particular station which has been registered.

Normal conditions-When there are no trains on the various track sections and the operator has established no routes for the passage of trains, all of the indicator lamps on the track diagram are deenergized, so that the control panel presents a dark board to the operator. The announcement of a train at any point is readily apparent by the illumination of the associated indicator lamp after which the operator by suitable positioning of his control levers may establish the desired route for the particular train indicated.

With reference more particularly to Fig. 2 of the accompanying drawings, the track relays T, T T and T are shown normally energized as is usual in common practice.

The signals l-lA and 2-2A are at stop, as the associated control relays lF-IAF and 2F--2AF are deenergized by reason of the positions assumed by the contacts of relay SR. in correspondence with control lever SGL. With the signals at stop, the relay M is energized through a circuit from through back contacts 30, 3|, 32 and 33 of relays IAF, IF, 2F and ZAF respectively, wire 34, winding of relay M, to

The track switch TS is in a normal position as last controlled by its switch machine (not shown) by reason of the position assumed by the contacts of relay SMR in correspondence with normal position of the control level SML.

With the traflic controlling devices in correspondence with the control relays SMR and SR, as they should be under normal conditions, the relay 0C is energized through a circuit traced from through back contact 35 of relay SL, wire 35, contact 37 of relay SMR in a right hand position, wire 33, contact 39 of relay WP in a right hand position, wire 40, front contact 4! of relay M, wire as, contact 43 of relay SR in a right hand position, wire 44, front contact 45 of relay WP, wire 46, back contact 41 of relay CL, wire 48, upper winding of relay O0, to

This energizing circuit for the relay 0C is completed only with the communication system at rest, as indicated by the relay SL. However, the relay 0C is maintained energized when the system is in operation, through a stick circuit from through front contact 49 of relay 00, wire to contact 37 and thence through the rest of the circuit as above traced. In other words, should the communication system be initiated into operation for the transmission of controls or the transmission of indications, thereby energizing the relay SL at the control oilice and at each field station, the relay 00 would remain energized through its stick circuit in spite of the opening of back contact 35, if the traific controlling devices at the station remain in correspondence with the associated control relays.

With reference more particularly to Fig. 1 of the accompanying drawings, the indicating relays IR give indications under normal at rest conditions that correspond to the positions of the control levers, thus the out of correspondence relay OC is energized through a circuit traced from through polar contact 55 of relay 1R in a right hand position, wire 56, contact 57 of relay 1R in a right hand position, wire 58, control contact 59 of lever SML in a normal position, wires 55 and El, contact 62 of lever SGL in an intermediate position, wire 63, contact 54 of relay 1R in a right hand position, wire 55, contact 66 of relay 1R in a right hand position, wire 61, winding of relay OC, to

As the track switch TS is in a normal position indicated in the control oflice by the relay IR in a normal position, the miniature track switch point ts is actuated to a normal position by means of the normal actuating coils i6 which are energized from through contact ll of relay 1R in a right hand position, coils 75, to

Transmission and display of track circuit indicati0ns.F0r convenience let us assume that a train proceeding in a west bound direction enters the east approach track section deenergizing the track relay T (see Fig. 2).

The deenergization of the relay T causes the momentary contact 15, in passing from an energized position to a deenergized position, to momentarily complete a circuit between its associated front and back contacts. This circuit momentarily energizes the change relay CH from through momentary contact 75 of track relay T wires 15, ll and F8, Winding of relay OH, to The change relay CE is thus sulficiently energized to close its front contacts, which completes a stick circuit from through back contact 1'9 of stepping relay 4, wires 80 and 81, front contact 82 of relay CH, wires 85 and E8, winding of relay OH, to Also in multiple with this stick circuit, positive energy is applied from ,through back contact 83 of relay SI, to wire 8!, and thence through the stick circuit as traced. With the change relay CH maintained energized, the communication system is initiated into operation to transmit indication of the fact that the relay T is deenergized.

The initiation of the communication system into operation energizes the relays SL at the control oifice and at each of the field stations, after which the step-by-step mechanisms at each location sequentially operate in synchronism. On each of the steps impulses are transmitted in accordance with the code call of the station in order to register this station in the control ofi'ice and select the station for transmitting indications. The registration of this station in the control office results in the energization of relay C while the selection of the field station for transmitting indications is indicated by the energization of relays SI and TR ter the selection of the field station and its registration in the control ofiice, the step-by-step mechanisms at the control ofiice and at this station continue to operate for the transmission of indication impulses. Thus, for the second part of the cycle, as the step-by-step mechanisms at this field station and at the control office continue to operate insynchronism, includingthe stepping relays c, 5, 6, l and 8, also the stepping each of the field stations.

relays d, e, f, g and it, local indicationcircuits are closed at the control oflice and at the selected field station. On each of the steps the indication circuits at the field station energize or leave deenergized the relay P which controls the energized condition of the series message circuit extending from the control ofilce through This message circuit includes the message relay M in the control ofiice which in turn determines whether negative or positive energy shall be placed upon the indication circuits local to the control ofice.

As the group selecting relay GS is deenergized prior to the initiation of the system into operation and remains deenergized during such operating cycle, for reasons hereinafter pointed out, although some change should occur in the condition of the trafiic controlling devices, the indications transmitted for this cycle under consideration are associated with the track circuit conditions adjacent this field station.

On the first indication step, the relay P is left deenergized, as the relay GS is deenergized with front contact 8 open. Thus, the relay M remains energized and places positive potential on the indication bus I during the message period of that step. The relay G8 remains deener gized although a circuit is traced from (B+), through front contact 8'? of relay M back con tact 88 of relay LR front contact 89 of stepping relay d, indication bus I5, wire front contact 0| of relay C wire 92, upper winding of group selecting relay GS" to (13+), because the same potential is applied to both of its terminals.

In other words, on this first indication step, the relay GS in the control office is left deenergized or is energized in accordance with the position of the group selecting relay GS at the particular field station which is selected. In this case, as the indications to be transmitted are in accordance with track circuit conditions at the field station of Fig. 2, the relay GS remains deenergized in correspondence with the relay GS.

Upon the second step, the relay P is energized, because of deenergized track relay T through a circuit from through back contact I55 of track relay T wire I56, back contact I5? of group selecting relay GS, wire P58, front contact I59 of stepping relay 5, back contact I08 of stepping relay 4, front contact I40 of relay TR, front contact I50 of relay SI, upper winding of relay P, to This results in the deenergization of relay M during the message period of that step which places negative potential upon the indicating relay 1R through a circuit traced from (B-) through back contact 8? of relay M back contact 83 of relay LR back contact 89 of stepping relay (1, front contact i i: of stepping relay e, indication bus I0, wire Si, front contact 98 of relay C wire 99, back contact I00 of relay GS, wire IOI, winding of relay 1R to center tap CN of the battery source.

This actuates the contact I02 of relay IE to a left hand position in which the relay SR is energized from through contact I02 in a left hand position, wires I03, I04 and I05, winding of relay SR to The energization of the relay SR causes the energization of the east approach indicating lamp EAL through a circuit from front contact I08 of relay SR wire I01, indicating lamp EAL, wire I08, back contact I00 of relay AS to the flashing bus 26 which is intermittently connected to through contact 25. Thus, the east approach indicating lamp EAL is caused to flash which informs the operator that a train has entered the associated track section in the field.

The indicating lamp ,EAL is insured of continued flashing until the operator actuates the cancelling key CK, regardless of the fact that the train might for some reason leave the associated track section. This feature is due to a stick circuit provided for the relay SR which is traced from through back contact I I2 of relay A51 front contact H3 of relay SR wires I04 and I05, winding of relay SR to When the operator acknowledges the flashing of indicator lamp EAL by depressing the cancelling key CK, the acknowledging stick relay AS is energized through a circuit traced from back contact II2 of relay AS front contact II3 of relay SR wires I04 and H4, winding of relay A8 wires II5, IIG, H1, H8 and H9, cancelling key OK in a depressed position, to

If the train has remained within the track section and is so indicated by relay 1R a multiple pick-up circuit is provided for relay AS from through contact I02 of relay 1R in a left hand position, wires I03, I04 and thence through the circuit as traced.

The energization of the relay AS is maintained by closure of a stick circuit only if the train has remained upon the track section causing the contactI02 of relay IE to remain in a left hand position. This stick circuit may be traced as follows: from through contact I02 of relay 1R in a left hand position, wires I03, I04 and. H4, winding of relay A8 wires H5 and I'20, front contact I2I of relay A8 to The energization of the acknowledging stick relay AS causes the indicator lamp EAL to be continuously energized by placing the continuous negative potential upon the wire I08 through front contact .I09.

However, if the train has left the associated track section and the contact I02 of relay IE is in a right hand position, relay AS is energized prior to the actual response of its contact and only partway through the operation of the contacts, although the cancelling key CK is maintained depressed. This is due to the opening of its ownenergizing circuit at back contact I I2. The relay AS is made slightly slow releasing to give sufficient time for the relay SR to drop away, which extinguishes the illuminated indicator lamp EAL.

Upon the remaining indication steps, the relay P is energized or is left deenergized, in accordance with the positions assumed by relays T, "I

and T in asimilar manner as explained for relay T In the case under consideration, these track relays are energized.

- Thus, the relay M in the control oiiice remains energized causing positive potential to be placed upon the relays IR, IR, and IE The contacts of the indicating relays IR, IR and IR therefore remain in their right hand normal positions, maintaining the indicator lamps OSL, WAL and PSLrespectively deenergized, as they are controlled in a similar manner as indicator lamp EAL.

Upon the energization of the stepping relay 4 at the way station, with the relay SI energized, positive energy is removed from the stick circuit of the relay CH by open back contacts I9 and 83. Thus, with the relay CH deenergized, the system returns to an at rest condition after completing the one cycle of operation.

Indications of trajfic controlling devices-The operator inthe control. ofiice acknowledges the presence of the-train upon the east approach section by depressing the cancelling key CK which results in a steady illumination of the indicator lamp EAL.

Assuming that the operator desires to route this train onto the turn-out track, he positions the switch machine lever SML in a reverse dotted line position and moves the lever SGL toa left hand dotted line position, after which he presses the starting button SE. The actuation of the starting button SB causes the communication system to be initiated intooperation and to operate through a cycle to transmit the controls established by the levers SML and SGL in a suitable manner to actuate the control relays SMR, SR and DR at the field station into correspondence therewith.

The out of correspondence relay 0C is now deenergized with contact 59 of lever SML in a reverse position out of correspondence with contact 51 of relay 1R which indicates the normal position of the track switch TS. Similarly, with the contact 62 of lever SGL in a right hand west bound controlling position which is out of correspondence with the stop condition of the signals indicated by the indicating relays IR and 13 the energizing circuit for the relay O0 is further opened. With the relay OC deenergized, the no route lamp NRL is illuminated by reason of a circuit from through indicating lamp NRL, wire I25, back contact I24 of relay 00, to The illumination of this no route lamp advises the operator that the trafiic controlling devices at the corresponding field station have not yet responded to the new positioning of the control levers.

Prior to the operation of the relays SMR, SR and DR, the field station must beselected which is indicated by the energization of the relays SO and TR. This results in the energization of the control relay CL from through front contact I26 of relay TR, wire IZ'I, front contact I28 of relay SO, wire I29, winding of relay CL, to

At the field station thus selected (see Fig. 2), the relays SMR, SR and DR assume their new positions so that the out of correspondence relay 0C is deenergized by reason of contact 31 of relay SMR being in a left hand dotted line position out of correspondence with the contact 39 of relay WP. Similarly, the circuit of the relay 0C is opened by reason of the contact 43 of relay SR being in a left hand dotted line position out of correspondence with the contact 4| of relay M.

The traffic controlling apparatus, including the track switch TS and the signal 2A, is operated in response to the controls transmitted to the relays SMR, SR and DR in accordance with the block signalling system and approach locking means associated therewith, in a manner set forth for example in the above mentioned patent to S; N. Wight, Patent No. 2,082,436 dated June 1, 1937.

However, no indications are transmitted to the control office as the relay GS is not energized until the traiiic controlling devices are operated into correspondence with their respective control relays. The only indication which might be desirable to be known by the operator is the fact that the track switch TS is in midstroke, which fact he may assume to be true inasmuch as the no route lamp NRL is still illuminated. If the operator desires an actual indication of the condition of the track switch, he may cause the system to repeat or check the indications as specifically pointed out hereinafter.

After this cycle of operation of the communication system, which transmits the controls to the control relays SMR, SR and DR, is completed, the. relay CL isi again deenergized. But during that cycle of operation, after the energization of relay CL and the deenergization of relay 00, the relay AX is energized from through back contact 49 of relay 00, wire I30, winding of relay AX, to so that the deenergization of the relay CL- at the'completion of the cycle does not actuate the relay GS. Considering that the track switch TS is operated to: a reverse locked position which is repeated by the relay WP, and that the signal 2A is cleared with relay ZAF energized which deenergizes" relay M, the energizing circuit for the relay 0C is closed. This energizing circuit for the relay 00, which is completed after the traffi'c controlling devices are in correspondence with their control relays, is completed only when the communication system is at rest, because the energization of the relay 0C completes a momentary pick-up circuit for the relay GS, later explained, which relay GS can not be energized during a cycle of operation as the transmission of track circuit indications might be erroneously interrupted. More specifically, this circuit is traced from through back contact 35 of relay SL, wire 36, contact 31 of relay SMR in a left hand dotted line position, wire I3I, contact 39 of relay WP in a left hand dotted line position, wire 40; back contact M of relay M, wire I32, Contact of relay SR in a left hand dotted line position, wire 44, front contact of relay WP, wire 46, back contact 41 of relay CL, wire 48, upper winding of relay DC, to

The energization of the relay 0C closes its stick' circuit at front contact 49, and opens the energizing circuit of the relay AX at back contact 49, but the relay AX is sufficiently slow acting to permit a momentary pick-up circuit to be completed for the relay GS. This momentary pick-up circuit for the group selecting relay GS is traced from through front contact I35 of relay OC, wire I36, front contact I3'i of relay AX, wires I38 -and I39, upper winding of relay GS, to This momentary energization of the relay GS actuates its contacts to energized positions closing a stick circuit from through back contacts I42 and I43 in multiple of the relays ST and'TR respectively, wire I45, front contact I46 of'relay GS, lower winding'of relay GS, to().

The energization of the relay GSinitiates the communication system into operation for the registration and the selection of this station. The operation of the system-causesrelaysSL and SE to be energized. At the end of the station selecting'part of the cycle, the station registerin'g relay C is energized in the control office, and the relaysSI and TR are energized at the field station;

The relay GS is maintained energized through the cycle of operation by the completion of another stick circuit by the relay SL prior to the energization of the relays SI and TR. This stick circuit for the' relay GS is traced from through front contact 35 of relay SL, wires I 40, MI and I 45, front contact I46 of relay GS, lower winding of relay GS, to

Upon the first indicating step of this cycle of operation, the relay P is energized from through front contact 84 of relay GS, wire I i'I, front contact I48- of relay 4, front contact I49 of relay -TR-,-front-contact I50 of relay SI,upper winding of relay P, to This results in the deenergization of the relay M, which places negative potential upon the relay (is by back contact 81 through a circuit as heretofore traced.

, As opposite potentials are in this case applied to the opposite terminals of the upper winding of the relay GS", its contacts are actuated to energized positions closing a stick circuit for the relay Gs from through lower winding of relay GS, front contact I5I, wire I52, front contact I53 of relay SL to Upon the next step, the relay P is energized in accordance with the position of the polar contacts of relay WP. As the track switch TS is in a reverse position and the polar contacts of the relay WP are in left hand dotted line positions, the relay P is energized from through contact I6I of relay WP in a left hand dotted line position, wire I62, front contact I51 of relay GS, Wire I58, front contact I59 of stepping relay 5, back contact I48 of stepping relay 4, front contact I49 of relay TR, front contact I59 of relay SI, upper winding of relay P, to Thus the relay M is deenergized, thereby placing negative potential upon the indicating relay IR This energizing circuit for the relay IR is traced from (B-), through back contact 81 of relay M back contact 88 of relay LR", back contact 89 of relay (1, front contact 96 of relay e, indication bus I6, wire 91, front contact 98 of relay C wire 99, front contact I99 of relay GS", wire I64, winding of relay IR to (CN) The application of negative potential to the relay 1R causes its contacts to be actuated to left hand dotted line positions. The actuation of contact TI to a left hand dotted line position energizes the coils I54 from contact H in a left hand dotted line position, coils I54, to This energization of coils I54 causes the miniature track switch point ts to be actuated to a reverse position.

Upon the next step, the relay P remains deenergized by reason of the open back contact I66 of relay WP, as the relay WP is energized in accordance with the reversed and locked condition of the track switch TS. Thus, relay M remains energized and places positive potential upon the relay IR through a circuit traced from (B+), front contact 81 of relay M, back contact 88 of relay LE back contacts 89 and 96 of stepping relays d and 6 respectively, front contact I61 of stepping relay indication bus I1, wire I68, front contact I69 of relay C wire I19, front contact III of group selecting relay GS", wire I12, winding of relay IE", to the center tap of the battery source indicated as (CN). The polar contact of the relay IR therefore remains in a right hand normal position.

Upon the next step, the relay P remains deenergized as both of the signal control relays IAF and IF are deenergized. Thus, the relay M remains energized placing positive potential on the indicating relay 1R through a circuit from (13+) through front contact 81 of relay M back contact 88 of relay LR, back contacts 89, 96 and I61 of stepping relays d, e and 1, front contact I13 of stepping relay g, indication bus I8, wire I14, front contact I15 of relay C wire I16, front contact I11 of relay GS", wire I18, winding of relay 1R to the center tap of the battery source indicated as (CN). The polar contacts of the relay 1R therefore remain in right hand normal positions.

Upon the next step, the relay P is energized by reason of the energized condition of the signal control relay 2AF through a circuit traced from through front contact I89 of relay ZAF, wire I8I, front contact I82 of relay GS, Wire I83, front contact I84 of stepping relay 8, back contacts I85, I86, I59 and I48 of stepping relays 1, 6, 5 and 4 respectively, front contact I49 of relay TR, front contact I59 of relay SI, upper winding of relay P, to Thus, the relay M is deenergized placing negative potential upon the relay 1R through a circuit traced from (B), through back contact 81 of relay M back contact 88 of relay LR back contacts 99, 96, I61 and I13 of stepping relays d, e, f and g respectively, front contact I99 of stepping relay h, indication bus I9, wire I9I, front contact I92 of relay C wire I98, front contact I94 of relay GS", wire I95, winding of relay 1R to the center tap of the battery source indicated as (CN). The polar contacts of the relay 1R are therefore operated to left hand dotted line positions.

The actuation of the polar contacts of relay IE to left hand dotted line positions completes the last indication which is necessary to indicate that the traffic controlling devices at the field station are in correspondence with their respective control levers upon the control panel. The relay 0C is now energized through a circuit traced from through polar contact 55 of relay 1R in a right hand position, wire 56, polar contact 51 of relay IR in a left hand position, wire I96, contact 59 of lever SML in a reverse position, wires 69 and 6|, contact 62 of lever SGL in a west controlling position, wire I98, contact 64 of relay 1R in a left hand dotted line position, wire 65, contact 66 of relay B in a right hand position, wire 61, winding of relay OC, to The energization of the relay 00 opens the energizing circuit of the no route lamp NRL at back contact I24.

The energization of the out of correspondence relay 00 completes the pick-up circuit for the west stick relay WS from through contact 55 of relay IR in a right hand position, wire 56, contact 51 of relay IR in a left hand position, Wire I96, contact 59 of relay SML in a reverse position, wires 69, I99 and 299, winding of relay WS, wires 29I and 2922, contact 293 of indicating relay 1R wires 294 and 295, front contact I24 of relay DC to The energization of the relay WS completes the energizing circuit for the west route lamp WRL from through front contact 296 of relay WS, Wire 291, indicator lamp WRL, to

The completion of the cycle is indicated by the deenergization of the relays SL at the control oflice and at each of the way stations. The deenergization of the relay SL (see Fig. 1) opens the stick circuit of the relay GS at front contact I53; similarly, the deenergization of the relay SL (see Fig. 2) opens the stick circuit of the relay GS at front contact 35, as the contacts of relays SI and TR are still in energized positions.

The operator now has the resultant route information displayed before him on the control panel. Immediately he notes the illumination of the west route lamp WRL and the presence of a train on the east approach by illumination of lamp EAL, as all other indications, associated with this track switch, are extinguished. The routing of the train may be further verified by noting the position of the miniature track switch ts.

The indicators on the control panel, associated With other controlled points, are also extinguished unless similar conditions have been established.

Priority 0 trcqfic controlling device indications.Let us assume that the train. on the east approach track section accepts the clear signal 2A and proceeds onto the detector track section, over the track switch TS, and onto the turn out track.

The occupancy of the detector track section deenergizes the track relay T which energizes. the storing relay ST from through back contact Zlt of relay T, wires 2!? and H8, winding of relay ST, to This relay is maintained energized through a stick circuit from through back contact 219 of cancelling relay CR, wire 229, front contact 22I of relay ST, wires 222 and 2|8, winding of relay ST, to The energization of the relay ST actuates a momentary contact 223 thereby energizing the change relay CH in a similar manner as explained inconnection with the track relay T The deenergization of the track relay T also causes the signal control relay EAF to be deenergized through the medium of the signalling system associated therewith. This deenergization of the relay ZAF causes the energizing circuit of the relay M to be closed at back contact 33; When the contact 4| of relay M thus assumes. an energized position, the pick-up cicuit and one stick circuit for the relay 0C is opened at back contact 4 l, which deenergizes this relay 0C considering the communication system to be at rest, to be transmitting controls to this or some other station, or to be transmitting indications from some other station. If the system is transmitting indications from this station (for example track circuit indications) then the relay SI is energized and the relay 0C is maintained energized through a stick circuit from through front contact ofrelay SL, wire MG, front contact I42 of relay SI, Wire 224, front contact 225 of relay 00, lower winding of relay CC, to

Assuming that the relay OC can bedeenergized, anenergizing circuit is completed for the group selecting relay GS during the interval of time required by the slow acting relay AX to be energized through back contact 49 of relay 0C. This momentary circuit is traced from through back contact 135 of relay 00, wire 226, back contact 228 of relay CL, wire 229, back contact I31 of relay AX, wires I38 and I39, upper winding of the relay GS, to The relay GS is maintained energized through its stick circuits as heretofore pointed out.

Assuming that the relays CH and GS become energized simultaneously, the communication system is initiated into operation by both relays simultaneously; but if the relays are energized at different times, the first relay becoming energized will effect the initiation of the system into operation.

Under normal operation the change relay CH and the group selecting relay GS are energized prior to the selection of the station for the transmission of the associated indications. With the relay GS energized it is evident thatthe indications associated with the traffic controlling devices at this station are transmitted first. Therefore, an additional stick circuit for the relay CH is closed with the relay GS energized, in order that the system will again be initiated into operation for the transmission of the new track circuit indications standing ready for transmission. This holding stick circuit for the relay CH. is traced from through front contact 236 of relay. GS, wires 2.3.1, 8,0. and 8!, front.contact.82.-

the polar contacts of relays IR and IR of relay CH, wires 85 and 18, winding of relay CH, to

With the relay GS energized and the communi cation system initiated into operation, indication impulses are transmitted in the usual manner as heretofore explained. During this particular cycle of operation, the new indication transmitted is the one related with the signal control relay- 2AF which is now deenergized. Thus, the indicating relay 1R receives positive potential operating its contacts to right hand positions. The energizing circuit for the relay O0 is thereby opened causing its back contact I24 to complete the circuit for the no route lamp NRL.

However, the west route lamp WRL is maintained energized by the west stick relay WS, which relay is. maintained energized through a stick circuit fromthrough contact 55' of relayIR in a. right hand position, wire 56, contact 51 of relay IR in. a left hand dotted line position, wire I96, contact 59 of lever SMI- in a reverse position, wires 60, I99and 200, winding of relay WS, Wires 20! and 2"], front contact 2 of. relay WS, wire 2|3, contact 2| 4 of lever SGL in a west controlling position, to

The relay WS is thus maintained energized so long asthe track switch TS is indicated asbeing in correspondence with the control lever SML, and the signal control lever SGLremains in its last operated position, regardless of the fact that a train may pass beyond the signal thereby putting that signal at stop which causes the corresponding indicating relay to indicate an at stop position. In other words, although the train moves onto the OS track section, in this case causing the signal 2A to go to stop, which through the medium of the communication system causes the contacts of. the indicating relay IE to be returned to right hand positions, the west stick relay WS is maintained energized. This maintains the west route lamp WRL illuminated telling the operator that the route will be clear for deenergized upon the first indicating step (relay 4? energized) with relay GS energized. The operating' cycle, thus initiated, is executed with the relay GS deenergized, thereby permitting the transmission of the track circuit indications.

During this cycle of operation, the system functions in a similar manner as above described for the transmission of track circuit indications. In other words, the track relays T and T govern the relay P upon their respective steps so as to control the polar contacts of the indicating relays IR, and IR respectively to left hand positions; while the track relays T and T 'govern the relay P upontheir respective steps so as to control respectively to right hand positions. This control of the relay by. the track relays is similar as explained for the track relay'T except in those cases where storing means is associated therewith, as in the case of track relay T.

For example, the relay P is controlled upon its respective step by the relay ST through a circuit from through front contact 232 of relay-ST, upper winding of cancelling relay CR, wire 233, back contact 234 of 'relay GS, wire 235,-

front contact: I86of stepping relay 6, back-'con- 75;

tacts I59 and I48 of stepping relays 5 and 4 respectively, front contact I49 of relay TR, front contact I50 of relay SI, upper winding of relay P, to The contacts (not shown) of the indicating relay IR are operated in accordance therewith to left hand positions.

The energization of the cancelling relay CR opens the stick circuit of the relay ST, thereby deenergizing the relay ST, if the detector track section is not occupied; but if the section is still occupied with the track relay T deenergized, then the relay ST will remain energized, so that a stick circuit is completed for the relay CR. from through front contact 232 of relay ST, lower winding of relay CR, front contact 235 of the relay CR, to This cancelling relay CR is maintained energized until the relay ST is deenergized by the picking up of the track relay T. In other words, if the relay CR were not energized after the transmission of the associated indication, the relay ST'would remain energized although the track relay T became picked up.

Thus, the relays ST and CR. provide means for storing the occupancy of the detector track section only until the communication system has operated to transmit the associated indication impulses. In a like manner, similar storing and cancelling relays could be employed with the track relays T I and T for accomplishing the same purpose with respect to the indications associated therewith.

The relay IR has associated therewith relays SR and AS for controlling the indicator lamp OSL in a similar manner as explained for indicator lamp EAL. With the contacts of relay IR in left hand positions, circuits are closed to thereby illuminate the OS indicating lamp OSL, which indication will be a flashing one until the operator actuates the cancelling key CK.

At the completion of this cycle of operation, the communication part of the system returns to an at rest condition, as the change relay CH is deenergized upon the energization of the first stepping relay as heretofore pointed out.

The train continues over the track switch TS onto the turn out track thereby deenergizing the track relay T Indication of this fact is transmitted to the control office in the manner which will be understood by analogy to the above description. This results in the illumination of the indicator lamp PSL, which gives a flashing indication until the operator actuates the cancelling key CK.

It is to be understood, that the transmission of the track circuit conditions has been explained for the entrance of the train only, but that similar transmission of track circuit indications occurs upon the departure of the train from each track section, that is, the change relay CH is also energized by the momentary contacts upon the energization of the respective track relays. This results in the return of the polar contacts of the corresponding indicating relay IR to right hand positions extinguishing the corresponding indicator lamps.

As long as the operator leaves the signal control lever SGL in either extreme position for clearing east or west bound signals, trains may follow each other with spacing provided by the automatic block signal system, provided of course that the particular signal, which is cleared thereby, is not what is termed a stick signal sometimes employed in certain cases. Each time a train passes and puts the cleared signal at stop, the no route lamp will be illuminated until the train passes beyond the governing track sections allowing the signal to again clear. If the particular signal cleared is a stick signal, it will remain at stop until the operator returns his control lever to a cleared position for such signal to clear. In such a case, the no route lamp will remain illuminated until the operator moves his control lever SGL to the stop position, after which the operation is similar to that already explained.

The functioning of the system has thus been described as including operation of the system in response to movement of control levers for the transmission of controls, together with the operation of the system resulting from the passage of a train through territory under the control of the operator. Although other combinations of train moves can be made, and other combinations of track lay outs may be controlled by such a system, it is to be understood that the particular example chosen was selected merely for making clear the most usual functions and features of the invention rather than the total number of combinations of operations which might occur in practice.

Operator may check indications.Let us assume that the system is in a normal condition, as shown in the accompanying drawings, and

that the operator desires for one reason or another to check the positions of the trafiic controlling devices at the field station.

To do this, it is only necessary for the operator to initiate the system into operation by actuation of the starting button SB without the movement of any control lever. The operation of the communication system is thereby initiated for the selection of the associated field station, which selection is determined by the energization of the corresponding relays SO and TR. The energization of these relays results in the energization of the control relay CL whichdeenergizes the out of correspondence relay 00 at back contact 41 of relay CL.

The deenergization of the relay 0C energizes the slow .acting relay AX, so that upon completion of the cycle of operation initiated from the control ofiice, the relay CL is deenergized, again completing the circuit for the relay 0C. During the time required for the slow acting relay AX to assume a deenergized position, after such energization of relay 0C, a circuit is completed for momentarily energizing the relay GS to thereby cause the system to be initiated for the transmission of the controlled device indications from that field station. This pick-up circuit for the relay GS is traced from through front contact I35 of relay 00, wire I36, front contact I31 of relay AX, wires I38 and I39, upper winding of relay GS, to With the relay GS energized the system is initiated for the transmission of indications.

In other words, this arrangement just pointed out provides that the operator may check the controlled device indications even though they are actually in correspondence with the control levers.

The system is also provided with means to enable the operator to check the controlled device indications of a field station, although the controlled devices are not in correspondence with their respective control levers.

Let us assume that the operator moves the signal control lever SGL to a clear position for one direction or the other, which results in the control of contact 43 of relay SR to a left hand position (see Fig. .2), and the deenergization of relay 0C. If the proper signal does not clear, due to the presence of a train or some other reason, the relay M will remain energized and the relay DC will not be energized subsequent to the control transmitted to relay SR.

The operator notes that the no route lamp NRL remains illuminated and desires to check the indications to see if it is a failure of the system to transmit or an actual condition at the field station. He actuates the starting button SB to select the corresponding station.

With the relays SO and TR energized after the selection of the station, the relay CL is energized. However, prior to the selection of the station, with the relays CL and OC deenergized, the slow acting relay BX is energized from through back contact 240 of relay CL, wire 24l, winding of relay BX, wire 242, back contact 243 of relay 0C, to Thus, as soon as the relay CL is energized, a circuit is completed for energizing the relay GS during the time that the slow acting relay BX is assuming its deenergized position. This momentary energizing circuit for the relay GS is traced from through front contact 240 of relay CL, wire 244, front contact 245 of relay BX, wires- 246 and I39, upper winding of relay GS, to The energization of the relay GS initiates the system into operation for the transmission of indications associated with the control devices, in a manner similar to that heretofore pointed out.

In other words, the system is provided with means for the operator to cause the controlled devices to transmit their indications regardless of whether they are in correspondence or whether they are out of correspondence with their associated control levers, without in any way changing the route conditions, by suitably causing the selection of the associated field station.

Summary-The centralized traffic control system herein shown and described as one embodiment of the present invention, provides information of the condition of the controlled devices and the presence of trains in a clear, concise and accurate manner.

In accomplishing this purpose, the present invention provides means for organizing and properly relating the indications with the controlled devices and the control machine, and also provides means for storing individual indications and certain groups of indications in order to insure their transmission and reduce the total number of operating cycles.

The invention also points out the advantages of grouping indications into groups that are of distinctive classes in that their transmission may be separated by several cycles of operation without impairing the facility of the system. However, it is to be noted in this connection, that although the grouping feature and the feature of storing or suppressing controlled device indications have been shown combined, it must be understood, they may be employed separately and still remain within the scope of the invention.

The system further provides that the operator may check the positions of the controlled devices at a field station, without either changing their positions or providing additional control steps, by means of selecting the station with or without the transmission of controls thereto.

Having thus shown and described a centralized traflic control system for railroads as one specific embodiment of the present invention, it is desired to be understood that this form is selected to facilitate in the disclosure of the invention rather than to limit the number of forms which it may assume; and, it is to be further understood that various modifications, adaptations and alterations may be applied to the specific form shown to meet the requirements of practice, without in any manner departing from the spirit or scope of the present invention except as limited by the appended claims.

Having described my invention, I now claim:

1. In a centralized traffic controlling system, a railroad track switch, a detector track section associated with said switch, a synchronous selector type communication system connecting said track switch to a central control office, means for causing a plurality of indications to be transmitted over said communication system during a single cycle of operations and means causing indications of the condition of said track switch and said track section to be transmitted over said communication system during different cycles of operation, whereby the length of each cycle of operation is reduced.

2. In a centralized trafiic controlling system, a control ofiice, a railroad track switch, signals governing traffic over said switch, annunciator track sections associated with said track switch, a synchronous selector type communication system connecting said track switch to said control oflice and automatically controlled for transmitting a plurality of indications during each cycle of operation, and means for automatically transmitting during any particular operating cycle of said synchronous selector communication system either the indications of said track switch and signals only or the indications of the conditions of said annunciator track sections only.

3. In a centralized trafiic controlling system, a control ofiice, a plurality of field stations, stepby-step means in the control oflice and at each field station operated synchronously, a message circuit extending from the control office to the several field stations, conditioning means at each field station for controlling the energization of said message circuit in accordance with a distinctive code call for that station, means in the control ofiice responsive to the respective conditions of said message circuit for registering the particular station having the most superior code call, and means at each station for determining which group of a plurality of groups of indications are to be transmitted after the corresponding station has been registered in said control oflice.

4. In a centralized traffic controlling system, a control oifice, a plurality of field stations, stepby-step means in the control 013506 and at each field station operated synchronously, a message circuit extending from the control oflice to the several field stations, station selecting means in part located at the control oflice and in part at each field station for determining the particular station which may employ said message circuit during a particular system of operation, a plurality of trafiic controlling devices, a plurality of track sections, route indicating means actuated in accordance with the condition of said plurality of trafi'ic controlling devices, annunciator indicating means actuated in accordance with the occupancy of said plurality of track sections, and means selectively causing said plurality of traffic controlling devices to transmit indications during. a particular operating cycle in preference to said plurality of track sections when both are ready to transmit indications at the beginning of a cycle of operation.

5. In a centralized traffic controlling system for railroads, a control ofiice, a field station, a selective type communication system operable through cycles of operation for transmitting impulses from said field station to said control ofiice, .a plurality of trafiic governing devices at said field station, a plurality of indication storing relays at said control ofiice corresponding to said traffic governing devices, means causing different groups of said traffic governing devices to transmit impulses in accordance with their condition to their respective indication storing relays on separate operating cycles when said trafiic governing devices assume new conditions, and means determining the sequence in which the various groups may transmit impulses on succeeding cycles of operation.

6. In a centralized trafiic controlling system, a control olfice, a field station, a communication system connecting said control office to said field station, a plurality of trafiic controlling devices at said field station, control means in said control ofiice for transmitting controls to any one or several of said traffic controlling devices, and indication means at said field station for automatically transmitting indications to said control ofiice of the condition of said trafiic controlling devices at that field station each time any one or several of said traffic controlling devices changes its condition in response to a control only when the changed conditions of all of such devices correspond respectively to the controls transmitted to such devices.

'7. In a centralized trafiic controlling system, a control oifice, a plurality of field stations, a communication system connecting said control office to each of said field stations, a plurality of trafiic controlling devices at each of said field stations, control means in said control office for transmitting control impulses to their respective trafiic controlling devices, indication means at each field station for automatically transmitting indication impulses to the control office of the condition of said traflic controlling devices when said devices have completetd their operation into correspondence with their respective control means, and means manually operable for causing said indication means to transmit indication impulses of the condition of said trafiic controlling devices independently of their condition with respect to their respective control means.

8. In a centralized traflic controlling system, a railroad track switch, signals indicating clear or stop for governing traffic over said switch in one direction, switch control means for governing operation of said track switch, signal control means for governing operation of said signals, a route indicator lamp for said one direction, means for illuminating said indicator lamp when said switch is in correspondence with said switch control means and said signals indicate clear in correspondence with said signal control means, and means maintaining said indicator lamp illuminated, when said signals are caused to indicate stop due to trafiic conditions, until said signal control means is operated into correspondence with said signals to stop.

9. In a centralized traflic control system for ailroads, a control ofiice, a plurality of field stations, a step-by-step mechanism in the control office and at each field station operated synchronously, control and message circuits extending to each field station, a plurality of traflic controlling devices at each field station, control means at the control office for transmitting control impulses over said control circuit to said trafiic controlling devices, transmitting means at each field station for transmitting indication impulses over said message circuit to said control oflice in accordance with the condition of said trafiic controlling devices for each change in the condition of said devices, and means preventing operation of said transmitting means when the condition of said trafiic controlling devices is changed in response to said control impulses said means being efiective only until all of said plurality of devices have responded to their respective control impulses.

10. In a centralized trafiic control system for railroads, a plurality of manually controlled devices said devices being controlled successively through the medium of a selector type system, and means indicating the condition of said devices through the medium of said selector type communication system only if said devices have all responded to their respective manual control.

11. In a centralized trafiic control system for railroads; a control ofiice; a field station; a communication system interconnecting said control office and said field station; a plurality of traffic controlling devices at said field station; control means at said field station for operating each of said trafiic controlling devices, said control means being manually governed from said control ofilce through the medium of said communication system; indication transmitting means for transmitting indications of the condition of said traflic controlling devices to said control ofiice, said indication transmitting means including means for causing indications to be transmitted only after all said traflic controlling devices are operated by their respective control means into correspondence therewith; and means for causing indications to be transmitted irrespective of the correspondence between said control means and their respective trafiic controlling devices only after said control means are manually governed in the same manner twice in succession.

12. In a centralized trafiic control system for railroads, a control office, a plurality of field stations, a plurality of trafiic governing devices at each of said field stations, a communication system for selectively transmitting control impulses to said trafiic governing devices at a particular field station during each operation when initiated from the control ofiice and for selectively transmitting indication impulses to said control oflice in accordance with the condition of said trafiic governing devices at a particular field station during each operation when initiated from that field station, manually operable means for initiating said system from the control office for the transmission of control impulses to a particular station, and means for initiating said system from a particular field station for the transmission of indication impulses to the control ofiice from that field station only after that field station has received the same control impulses during a second operation.

13. In a centralized trafiic control system for railroads, a railroad track switch, signals capable oidisplaying proceed or stop indications for governing traffic over said switch in one direction, switch control means for governing operation of said track switch, signal control means for governing operation of said signals, switch indication means for indicating the position of said track switch, signal indicating means for indicating whether said signals are displaying proceed or stop indications, a directional stick route relay, a pick-up circuit for said directional stick route relay closed only when said switch control means and said switch indication means are in correspondence with said signal control means in a condition for causingsaid signals to display a proceed indication and said signal indicating means to indicate such proceed condition of said signals, a stick circuit for said directional stick route relay closed only when said switch control means and. said switch indication means are in correspondence with said signal control means still remaining in its previous condition as set up for causing said signals to indicate proceed, and an indicator controlled by said route relay.

14. In a centralized trafiic control system for railroads; a control oifice; a plurality of field stations; a plurality of traiiic controlling devices at 'each field station; control levers in the control office for each of said trafiic controlling devices; a selective type communication system connecting said control office with said field stations; means for transmitting controls in accordance with said control levers to said trai'hc controlling devices at each station, one station at a time; and means at each station for transmitting indica tions of the condition of the tran'ic controlling devices at each field station to the control office only after all said traffic controlling devices have responded to said controls, said means including means for transmitting indications irrespective of the response of said trafiic controlling devices if the same controls are transmitted twice to the same traffic controlling devices at a particular station.

15. In a centralized tramc controlling system, a railroad track switch, a switch machine for operating said track switch, signals for governing trafiic over said track switch, a switch control lever for governing operation of said switch machine, a signal control lever for governing operation of said signals, a route lamp for indicating when said track switch is in correspondence with said switch control lever and said signals are in correspondence with said signal control lever, and an additional lamp for indicating when either said track switch or said signals are out of correspondence with their respective levers.

16. In a centralized trafiic controlling system, a railroad track switch, a detector track section associated with said switch, a synchronous selector type communication system connecting said track switch to a central control oflice, means for causing a plurality of indications to be transmitted over said communication system during a single cycle of operations, means causing said indications of the condition of said track switch and said track section to be transmitted over said communication system during different cycles of operation'whereby the length of each cycle of operation is reduced, and means responsive to a condition requiring the transmission of both track switch and track section indications for causing said system to transmit said track switch indications first.

1'7. In a system of centralized traffic control for railroads, a control panel in the central ofiice having thereon a track diagram representing the portion "of the railroad under control, a manually movable switch control lever and an indicator associated with each track switch on the diagram, a code type communication system for governing the operation of the several switches in accordance with the position of their respective control levers and also transmitting to the central office indications reflecting the normal position, the reverse position and the unlocked condition of said respective switches, indicating means in the control oiiice responsive to the switch indications thus transmitted, and means for displaying the indicator associated with each switch lever whenever that lever is in a position out of correspondence with the last indicated position of the corresponding switch and whenever said unlocked condition of said switch is transmitted.

18. In a centralized traffic control system for controlling the operation of a power operated track switch from a central ofilce and for indicating in said central office the position and locked condition of said switch, the combination with indicating means responsive to the position and locked condition of the track switch, of a manually operable lever for controlling said switch, and an indicator associated with said lever and controlled jointly by said lever and said indicating means so as to be displayed whenever said lever is in a position out of correspondence with the position of the track switch or whenever the track switch is unlocked.

19. In a centralized trafiic control system, the combination with a communication system of the multiple impulse type, of a power-operated track switch, a manually movable lever in the central office forgoverning the operation of said communication system to control the operation of said track switch, indicating means responsive during the operation of said communication system to the position and locked condition of said track switch, and an indicator associated with said lever and controlled jointly by'saicl lever and said indicating means, said indicator being displayed whenever said lever is in a position out of correspondence with the last indicated position of the track switch manifested by said indicating means or whenever said indicating means is in a condition corresponding with the unlocked condition of the track switch.

20. A control panel for centralized trailic control systems comprising, a track diagram, a manually movable lever for each power-operated track switch, an out-of-correspondence lamp for each switch .lever, and means for always steadily lighting any particular one of said lamps whenever the corresponding track switch is unlocked or is in a locked position out of correspondence with the position of the associated switch lever.

21. In a remote control system of the character described, the combination with a power-operated track switch at a field location, of a control panel at a control office including a switch control lever for governing the operation of said track switch and a movable miniature switch point and. an indicator associated with said lever on the control panel in the control office, an indicating means in the central office automatically operated over line wires in accordance with the position of the track switch in the field, said indicating means automatically operating the miniature switch point, and means for illuminating said indicator jointly controlled by said indicating means and said switch control lever, said indicator being illuminated whenever the position of the track switch in the field manitested by said indicating means does not match the position of said control lever.

22. In a centralized traffic control system, a power-operated track switch, a control lever in a central omce, a miniature switch point at the central oifice, indicating means in the central office automatically responsive to the position and locked condition of said track switch, means controlled by said indicating means for operating said miniature switch point to a position correspending with said track switch, and an indicating lamp lighted whenever said indicating means shows that the track switch in the field is in a position out of correspondence with the position of said control lever, or is unlocked.

23. In a system of centralized trafiic control for railroads, a control panel in the control ofii ce having thereon a track diagram representing the track layout with miniature switch points representing the track switches, manually operable levers on said control panel for governing the operation of the switches and signals associated with the track layout, an out-of-correspondence lamp associated with each miniature switch point on the control panel, indication means in the control office for indicating the position and locked condition of each of the track switches in the field, and means controlled jointly by said indication means and said control levers for lighting a particular one of said out-of-correspondence lamps whenever the position of the corresponding track switch, as manifested by said indication means, is out of correspondence with the control set up for that track switch by said levers, said means also lighting a particular one of said out-of-correspondence lamps whenever said indication means indicates the unlocked condition of that track switch.

24. In a remote control system for railroads, a track switch having a normal closed position and a reverse closed position, control means operable from a remote point for moving said switch from one closed position to the other, indication means responsive to each change in position of said switch for indicating at said remote point whether the switch is closed or open, and means rendered effective when said control means is operated for preventing the transmission to said remote point of the open indication of said switch provided the switch is opened in response to the operation of said control means.

25. In a remote control system for railroads, a track switch having a normal closed position and a reverse closed position, control means operable from a remote point for moving said switch from one closed position to the other, indication means responsive to each change in position of said switch for indicating at said remote point whether the switch is closed or open, means rendered effective when said control means is operated for delaying the transmission to said re mote point of an indication of the position of the switch until the switch completes its movement in response to the operation of the control means provided the switch is closed when the control means is operated, and for causing an immediate transmission of an open indication of the switch provided the switch is open when the control means is operated.

26. In a remote control system for railroads, a track switch having a normal closed position and a reverse closed position, control means operable from a remote point for moving said switch from one. closed position to the other, indication means responsive to each change in position of said switch for indicating at said remote point whether the switch is closed or open, means rendered effective when said control means is operated for causing the indication means at said remote point to be controlled when the switch completes its movement in response to the operation of the control means provided the switch is closed when the control means is operated, and to cause the indication means to indicate that the switch is open only when the switch has been opened prior to said operation of the control means.

27. In a centralized traific control system for railroads, a control office and a field station, a normally-at-rest multiple impulse code type communication system connecting the control oflice and field station, a plurality of trafiic controlling. devices at the field station, control relay means at the field station for each of said traflic controlling devices for controlling the operation of such devices, manually governed means at the control ofiice for initiating said communication system and transmitting control impulses to said control relay means through the medium of said communication system, means at the field station for transmitting indication impulses to said control office through the medium of said communication system in accordance with the condition of said traflic controlling devices when the communication system is initiated into operation, and means requiring all of said traffic controlling devices to operate into correspondence with their respective control relay means for initiating said system into operation to transmit indication impulses.

28. In a centralized trafilc control system for railroads, a normally-at-rest code type communication system connecting a control ofilce and a field station, a plurality of trafiic controlling devices at the field station, a control relay at the field station for each of said traffic controlling devices for governing its operation, means at the field station causing said control relays to be responsive to control codes transmitted over said communication system, means at the control oflice for initiating and transmitting control codes over said communication system, means at the field station for transmitting indication codes over said communication system in accordance with the conditions of the several traffic controlling devices when said communication system is initiated into operation at the field station, means for initiating said communication. system into operation at the field station, said means requiring all of said trafiic controlling devices to operate into correspondence with their respective control relays, andmeans for initiating said communication system into operation when any one or all of said devices operates out of correspondence with its respective control relay.

29. In a centralized trafiic control system for railroads, a normally-at-rest code type communication system connecting a control office and a field station, a plurality of trafiic controlling devices at the field station,a control relay at the field station for each of said traffic controlling devices for governing its operation, means at the field station causing said control relays to be responsive to control codes transmitted over said communication system, means at the control office for initiating and transmitting control codes over said communication system, means at the field station for transmitting indication codes over said communication system in accordance with the conditions of the several traflic controlling devices when said communication system is initiated into operation at the field station, a correspondence relay controlled by said traffic controlling devices and their control relays so as to indicate when all of said devices are in correspondence with their control relays and when any one or all 

